Process for making packs for electrical heating units



Patented Mar. 24, 1925.

UNITED STATES PATENT OFFICE.

WILLIAM A. BRAUN, OF DOVER, OHIO, ASSIGNOR T DOVER LIANUFACTURING COM-PANY, A CORPORATION OF OHIO.

PROCESS FOR MAKING PACKS FOB. ELECTRICAL HEATIN G UNITS.

Io Drawing.

To all whom, it may concern:

Be it known that I, 'ILLIAM A. BRAUX, a citizen of the United States ofAmerica, and a resident of Dover, in the county of Tuscarawas and Stateof Ohio, have invented certain new and useful Improvements in Processesfor Making Packs for Electrical Heating fnits, of which the following isa specification.

This invention relates to improvements in processes for making packs forelectrical heating units and the object thereof is the provision of adense encasement. for electrical resistance members, having highdielectric and low hygroscopic properties and great thermalconductirity.

In general practice packs are formed in which electrical resistancemembers are embedded, which are composed of a mixture 0 of variousmaterials and which are 'subjected to great pressure and intense heat inorder to effect solidification of the mas The porosity of packs thusformed'is such that their tendency to absorb or become 5 coated withmoisture impairs their di-electric property especially during periods ofdisuse which results in grounding of the electrical current when theresistance members are charged upon resumption of their use.

The present invention contemplates the formation of a tenacious pack inwhich the (Ii-electric and thermal eomluctivity then-of will beindefinitely preserved. as The objects of the invention are accomplishedby the use of materials compounded and applied as hereinafter set forth.

The invention consists in a proce of forming an encasement forelectrical resist- 4o ance members utilized in connection withelectrical heating units, and by means of which the (Ii-electricproperty and thermal conductivity of the pack will be enhanced andpreserved indefinitely.

In carrying out the invention a pack of usual form is made of a plasterconstituted of a mixture of refractory material. clay and boracic acidmoistened with water. The components of the plaster are approximate-Application filed January 5, 1923. Serial No. 610,945.

ly in relative proportions as set forth in the following tabulation:

Percent. Refractory material 83 Clay 12 Boracic acid -c 5 The refractorymaterial employed is such as Alundum fines commonly known in the art, ormay be such other hard, granular or mlrerulent material of similarcharacter 00 which is possessed of high thermal conductivity and highdi-electric properties.

The clay herein used as an agent for holding the pulverulent refractorymaterial suspended in the mixture when the mixture is moistened and in aplastic state, may be of any suitable character, such. for example, asKlingenberg clay, which has been found satisfactory- The boracic acid,when introduced into the mixture, is in powdered form and in the stateknown as H 130 In preparing the plaster. the ingredients are placed in apebble mill with water approximately equal in quantity to half of theamountof powder. by weight,:u1d therein is ground and worked into aplastic mass. The composition thus formed is then placed in a suitablemining machine and agitated until used.

The plaster is molded or formed into a pack in a mann r to em ed theresistance wire of the heating clenn-nt so that the resistance wire iscompletely encased hy the pack. After thus being formed the pack isdried until it becomes hard and is then raised to the normal workingtemperature of the heating element in which it is used. This heatingoperation may he carried out by charging the resistance wire initiallywith electric current of only sullicient strength to heat the resistancewire to its working temperature. When the pack thus heated the l'oracicacid constituent of the mixture of which the pack composed, becomesmelted, forming horic oxide (B 0 which saturates the pack during theinitial heating thereof so that the granular partitracted.

The constituents of the plaster and their relative proportions, setforth herein as an example of the invention, are subject to suchsubstitutions and variations of proportions as skill in the art affords.and therefore, my invention is extensive thereto. Also other methods ofinitially heating the pack may be substituted for the particular mannerdescribed herein.

\Vhat I claim is 1- 1. The hereindescribcd method of making packs forelectrical resistance members consisting of mixing pulvcrulentrefractory material, clay and boracic acid substantially in theproportions named herein, forming a plaster by adding water to themixture, encasing a resistance member in a pack formed of the plaster,drying the pack, and finally reducing the boracic acid content of thepack to boric oxide without melting the refractory material, byinitially heating the member only to its working temperature whereby thesaid member and the particles 1 of material surrounding the memberbecome intimately coated with said oxide.

2. In making a pack of pulverulent rcfractory earthen material forencasing an electrical resistance member, the inclusion of boracic acidwith the material of which the pack is formed, charging the resistancemember initially after the pack has been formed with electrical currentof sutticient strength only to heat the resistance member suflicientlyto convert the boracic acid content of the pack into boric oxide andcause an intimate coating thereof to form on the member and the earthenparticles of the pack without. melting said member and particles.

3. In making a pack of pulverulent refractory earthen material forencasing an

